High levels of Co and Nox during inspection

Is there any way that I can get these levels normal so it will pass inspection. Mechanic said it will cost about 500 dollars

Did you change the oil and give it a tune up before the test? It may need a catalytic converter.

Smog inspections are always scarey. You think your car is running perfectly and then the smog hammer hits you right between the eyes. There are many things that could cause high CO and NO. There are tests that can be run which will point you in the right direction for a fix. The first thing is to make sure you have a clean airfilter, new spark plugs and spark plug wires if they are old. Then it is time to do some testing. Plugged EGR system can cause high NO and the test involves testing the EGR valve to see if that is working and the intake ports are clear. O2 sensor could be a problem as well as a cat. converter. However if you start replacing all those things without pinpointing the problem it could cost as much as the car is worth if the car is old. By the way, what year and model are we taking about.

Smog inspections are always scarey. You think your car is running perfectly and then the smog hammer hits you right between the eyes. There are many things that could cause high CO and NO. There are tests that can be run which will point you in the right direction for a fix. The first thing is to make sure you have a clean airfilter, new spark plugs and spark plug wires if they are old. Then it is time to do some testing. Plugged EGR system can cause high NO and the test involves testing the EGR valve to see if that is working and the intake ports are clear. O2 sensor could be a problem as well as a cat. converter. However if you start replacing all those things without pinpointing the problem it could cost as much as the car is worth if the car is old. By the way, what year and model are we taking about.

Good advice...

If your test is done on a dyno (in gear, wheels in motion), one would almost have to see the actual testing trace report (that shows RPM, speed and time on a graph) to get a handle on possible causes.

For instance, like mpumas said, NOx emissions come from excessively hot combustion, which the EGR is there to help minimize. When it doesn't work right, NOx emissions will be high, especially during hard acceleration under load, so you'll usually see it spike best when the throttle is opened wide while running in top gear...but a NOx spike when the throttle is snapped shut can indicate other problems...increased cylinder pressure from carbon loading (a side effect of overly rich condition) can also increase NOx levels.

High CO usually points to an overly rich (excess fuel) condition, but rich also cools the combustion down, which lowers NOx levels...so many times when you correct the lean condition causing high CO readings, NOx levels rise...this is why it's so important to see the trace report...have to see how the two failing readings relate to each other and what's going on at the time.

If you get it repaired at a shop, ask them to explain the readings, why they think they need to do what they propose to fix it, etc.

If it's a case where they are just doing the required amount of repair attempt to be able to waiver it or something, be skeptical...it probably won't solve anything, and will bite you again next test, in a year or two or whatever your state requires.

PS if your EGR valve is vacuum operated, a leak in the vacuum line that operates it could account for both problems...worth a look...

I would start from cleaning the EGR port. Also, if the EGR is controlled by a VSV, check if the VSV functions well.

I recommend not shotgunning replacing/repairing items unless you know they are defective. Honda has a specific testing procedure for checking the EGR system which includes disconnecting the vacuum line to the EGR valve attaching a vacuum pump to the valve and drawing a vacuum, clamping the hose and seeing if the EGR will hold the vacuum. In this condition, if the ports are clear, the engine will not run in idle.

I recommend not shotgunning replacing/repairing items unless you know they are defective. Honda has a specific testing procedure for checking the EGR system which includes disconnecting the vacuum line to the EGR valve attaching a vacuum pump to the valve and drawing a vacuum, clamping the hose and seeing if the EGR will hold the vacuum. In this condition, if the ports are clear, the engine will not run in idle.

I used the poor man's method....

Put a piece of new vacuum hose on the EGR, use your mouth to suction the valve open, stick your tongue on the end of the hose, sealing it, and see if the EGR (or other vac item, servo, choke pull-off, etc) stays open, and like you said if the engine stalls from idle when the EGR is opened.

Work in a low-tech shop long enough, you figure out all kinds of ways around normal test procedures...:lol:

Anyway, what mpumas is getting at is if the ports are clear and clean, opening the valve creates a massive vacuum leak that will stall an idling engine...if the ports are hogged up with carbon, the motor will continue to run as if nothing happened when you open the EGR valve...

also do you have any upgrades? any sort of intake mod? I've had three different vehicles with cone style intakes fail on the nox section. Someone told me that because there was more air going in (which i wanted obviously) it was burning too hot, so find a way to obstruct some of the air. I took the piece of paper that said I failed and wrapped it around the cone filter and duct taped it. lol I didnt want to remove the cone filter i just bought. haha Well anyways went back through the DEQ and passed every time with all three vehicles. They were an '89 Accord LXi Sedan, '92 Acura Vigor and an '86 Bronco II. Hope its helps, oh then once i passed i removed the paper.

NRPalmer...shouldn't intakes decrease emissions? I read somewhere that intakes trick the engine into thinking it is not sucking in enough air, so it will lean out...don't know if that's true either.

Anyways, mpumas and jeffcoslacker brought up very interesting points. I should test my egr soon.

NRPalmer...shouldn't intakes decrease emissions? I read somewhere that intakes trick the engine into thinking it is not sucking in enough air, so it will lean out...don't know if that's true either.
Well the comp should compensate for the more air going through the sensors so it should be adding more fuel, you are right. I'm not sure why exactly it worked on three different vehicles but it has so I keep doing it. lol If anything, try it and if it doesn't work then just try something else.

Thread a bit old but here is some good info for anyone coming thru this thread on a search.


jeff explained it best, and I think that was what the OP was asking, the specific causes of why one particular output gas would be high, here's a really good reference for exhaust gas analysis:

http://www.autoshop101.com/forms/h56.pdf

I took my car to the emissions place last year b/c I was having trouble with it, asked him to do an exhaust gas test (he's had the friggin exhaust sniffer equipment!) so I can use the results to help pinpoint my problems... he thought I was insane.

Maybe I should print this out for him?